I think under the law of property there is no time limit so if your Van Gogh painting was stolen in 1960 and subsequently found in the year 2020, it is still yours. My suggestion is, assuming the vehicle is actually stolen is to make the MOD a reasonable offer to own it and recover it from its location, which I guess they would agree. It would possibly cost them more to do the recovery. In 2007 the MOD sold EE Canberra jets for c £1 as long as the owner paid for the removal.